a. Field of the Invention
This invention relates generally to the field of signal processing, and more specifically to pulse amplitude modulators for use in the analog-to-digital and digital-to-analog conversion of a signal by the process known as continuous variable slope delta (CVSD) modulation.
B. Description of the Prior Art
Continuous variable slope delta modulation and pulse amplitude modulators for use therein are known in the prior art. CVSD is an analog-to-digital and digital-to-analog conversion technique which exploits the syllabic characteristics of speech to minimize the number of bits required in its digital representation. Because CVSD is a mono-bit system, the coding and decoding processes do not require timing information of a higher order than for recovery of the individual bits. That is, unlike in such techniques as pulse code modulation, framing information is not required. Two elements normally associated with the CVSD system include what will be called in this description a slope command and a pulse amplitude modulator. Prior art embodiments of these elements require an operational amplifier, balancing potentiometers, and various configurations of resistors, capacitors and control voltages. Those prior art pulse amplitude modulators known to the inventor require at least two control voltages and consume significant amounts of power.